4.6 GEOLOGY AND SOILS

Transcription

1 4.6 GEOLOGY AND SOILS Coal mine tunnels and associated ventilation shafts may be located beneath the northwest portion of the project site. These mine ventilation shafts could jeopardize the safety of construction workers and individuals on the project site, representing a potentially significant impact. Mitigation measures have been included to reduce this impact to a less-than-significant level. Three abandoned dry oil/gas wells identified at the project and eight abandoned oil/gas wells identified in or in close proximity to the proposed utilities and transportation corridor pose a potentially significant hazard to the construction workers during project development. Mitigation measures have been included to reduce this impact to a less than significant level. Impacts related to seismically-generated ground shaking, liquefaction, slope failure, and subsidence on development infrastructure, structures, and individuals on the project site would be less than significant. Impacts related to soil erosion, expansion, and corrosion would be less than significant. No significant mineral resources have been identified on the project site. Development of the project would therefore have a less than significant impacts on mineral resources. This section describes the geologic conditions of the project site based on readily available geotechnical and geological literature, previous geotechnical investigation reports, and geologic maps. This section also assesses potential impacts from surface-fault rupture, ground shaking, liquefaction, slope failure, differential settlement, soil erosion, caving, expansive soils, corrosive soils, mining collapse, oil and gas wells, and mineral resources. Mitigation measures for the identified significant impacts are provided, as appropriate. This section evaluates impacts to geologic resources within the project site and proposed utility corridors along Empire Mine Road and Deer Valley Road. As discussed in Chapter 3.0, Project Description, extension of the utility lines from Heidorn Ranch Road to Deer Valley Road have been evaluated as part of the Aviano Adult Community Project EIR (2008) and are not included as part of this analysis EXISTING SETTING Existing Conditions Project Location and Setting The project site is located in the eastern Coast Ranges Geomorphic Province of northern California. The regional structure of the Coast Ranges consists of northwest-trending folds and faults associated with the San Andreas Fault Zone (SAFZ). As a result, 4.6-1

2 northwest-trending ranges of low mountains and intervening valleys dominate this region. In general, the Coast Ranges are composed predominately of sedimentary bedrock. 1 The project site is located in Horse Valley, which drains southeast toward Deer Valley Road and then northeast to Sand Creek and Marsh Creek. 2 The topography is relatively flat in the central and eastern portion of the project site along the valley floor and moderately steep along the ridges of the valley in the south and west portions of the project site. North of Horse Valley, the ridge crest elevation is approximately 400 feet (National Geodetic Vertical Datum of 1929 [NGVD]); south of Horse Valley, the ridge crest elevation is over 700 feet NGVD. The floor of Horse Valley ranges in elevation from approximately 250 to 350 feet NGVD. 3 The existing 230-acre Roddy Ranch Golf Course is located on the northern slopes of the ridge south of Horse Valley at the project site. The remainder of the project site consists of open grassland with scattered oak trees and brush. The proposed utilities and transportation corridor extend approximately 8,000 feet north of the project site and stretches up to about 500 feet wide, as shown on the Utilities and Transportation Corridor Map (Figure 3.7). Site Soils and Bedrock Geology The bedrock formations underlying the project site are mapped as Tertiary-age Meganos and Domingene formations. Outcrops indicating unique geological features are not apparent at the project site. The Meganos Formation, which underlies the ridges south of Horse Valley, is divided into an upper member consisting of biotite-rich siltstone and silty mudstone, and a sandstone member consisting of medium-grained sandstone. The ridges north and west of Horse Valley are underlain by the Domingene Formation, consisting of sandstone with minor mudstone and conglomerate. The bedrock formations generally dip down to the northeast at angles of approximately 15 to 35 degrees. 4 The Domingene Formation contains veins of lignite coal (low-grade coal) that were mined immediately north of the project site from approximately 1860 to Mining activities in the project site vicinity are further discussed below. The utilities and road improvements are proposed to extend north of the project site into Lone Tree Valley, as shown in Figure 3.7. Bedrock formations underlying portions of the utilities and transportation corridor include the previously discussed Domingene Formation and the lower member of the Markley Formation. The lower member of the 1 California Geologic Survey, United State Geological Survey, Ibid. 4 Graymer et al., Norfleet Consultants, 2006a

3 Markley Formation consists of thin-bedded to massive sandstone with minor siltstone and mudstone. 6 The Horse Valley floor is underlain by Pleistocene-age alluvial fan and fluvial deposits consisting of dense gravely and clayey sand or clayey gravel that fines upward to sandy clay. The Lone Tree Valley floor is underlain by Holocene-age alluvial fan and fluvial deposits consisting of medium-dense to dense gravely sand or sandy gravel that generally grades upward, to sandy or silty clay. 7 Clays and loam are located on the lower ridge slopes of Horse Valley and loamy sands are located on the upper ridge areas north, south, and west of the valley floor. 8 Seismic Hazards The project site is located near the eastern edge of the SAFZ. The SAFZ includes numerous active faults identified by the California Geological Survey (CGS) under the Alquist-Priolo Earthquake Fault Zoning Act to be active (i.e., to have evidence of fault rupture in the past 11,000 years). The United States Geological Survey s (USGS) Working Group on California Earthquake Probabilities estimated that there is a 62 percent probability that a 6.7 or greater magnitude earthquake will occur in the San Francisco Bay Area between 2002 and Major active faults in the region of the project site include the Greenville, Concord-Green Valley, and Calaveras faults. Regional active faults and historic earthquakes located in the vicinity of the project site are shown in Figure Surface Fault Rupture Surface rupture occurs when the ground surface is broken due to fault movement during an earthquake. The location of surface rupture generally occurs along an active fault trace. The CGS delineates the boundary of Alquist-Priolo Earthquake Fault Zones, which are about one-quarter mile around a known active fault trace. 10 The Earthquake Fault Zones indicate areas with potential surface fault rupture hazards and specific geological investigations are required prior to development. The project site is not located within or adjacent to an Earthquake Fault Zone. The nearest Earthquake Fault Zone is located along the Greenville Fault approximately 5.5 miles southwest of the project site Graymer et al., 1994, op. cit. 7 Helley and Graymer, United Stated Department of Agriculture, United State Geological Survey, California Geological Survey, Association of Bay Area Governments (ABAG),

4 Strong Seismic Shaking Ground shaking is a general term referring to all aspects of motion of the earth s surface resulting from an earthquake, and is normally the major cause of damage in seismic events. The extent of ground shaking is controlled by the magnitude and intensity of the earthquake, distance from the epicenter, and local geologic conditions. The magnitude of a seismic event is a measure of the energy released by an earthquake; it is assessed by seismographs that measure the amplitude of seismic waves. The intensity of an earthquake is a subjective measure of the perceptible effects of a seismic event at a given point and varies with distance from the epicenter and local geologic conditions. The Modified Mercalli Intensity Scale (MMI), as shown in Table 4.6-1, is the most commonly used scale to measure the subjective effects of earthquake intensity. Intensity also can be quantitatively measured using accelerometers (strong motion seismographs) that record ground acceleration at a specific location, a measure of force applied to a structure under seismic shaking. Historically, numerous moderate to strong earthquakes have been generated in northern California by several major faults and fault zones in the SAFZ system. In addition to the known active faults, which are recognized under the Alquist-Priolo Earthquake Fault Zoning Act, there are other potential sources of large magnitude earthquakes in the region. A structural trend of folds and thrust faults has been mapped in the hills southwest of the project site. 12 The largest of these features is the Mount Diablo anticline, which has been interpreted as a large fold developed above a buried (blind) thrust fault. The accumulation of strain on the blind Mount Diablo Thrust Fault presents the potential for an earthquake along this structure. 13 The USGS Working Group of California Earthquake probabilities considers the blind Mount Diablo Thrust Fault capable of generating a magnitude 6.7 or greater earthquake with an estimated three percent probability of it occurring during the period from 2002 to An earthquake of magnitude 6.7 along the Mount Diablo Thrust Fault is estimated to be capable of generating strong to very strong ground shaking (MMI-VII and -VIII, respectively) in the vicinity of the project site (Table 4.6-1). 15 An earthquake on that fault would not be expected to cause fault rupture at the surface and is not, therefore, identified by the Alquist-Priolo Earthquake Fault Zoning Act. 12 Crane, Unruh, United State Geological Survey, 2003, op. cit. 15 ABAG, 2004a

5 MAACAM FAULT HEALDSBURG-RODGERS CR. FAULT SAN ANDREAS March 31, 1898 M6.2 FAULT GREEN VALLEY ANTIOCH FAULT FAULT CONCORD FAULT HAYWARD FAULT June, 1835 M6.8 PROJECT SITE Pacific Ocean Oct 21, 1868 M7.0 GREENVILLE FAULT April 18, 1906 M7.8 CALAVERAS June, 1838 M7.0 SAN ANDREAS Nov 26, 1858 M6.4 July 1, 1911 M6.6 April 24, 1984 M6.4 SAN GREGORIO Oct. 8, 1865 M8.3 FAULT Feb. 26, 1864 M5.9 Aug. 6, 1979 M5.9 Oct. 18, 1989 M6.9 Aug. 6, 1979 M5.9 FAULT FAULT SM whole view. Source: California Division of Mines and Geology, 1987 FIGURE REGIONAL FAULT MAP 2672_

6 Table 4.6-1: Modified Mercalli Intensity (MMI) Scale MMI Scale Description I II III IV V VI VII VIII Not felt except by a very few under especially favorable circumstances. Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing. Felt quite noticeably indoors, especially on upper floors of buildings, but many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibration like passing of truck. Duration estimated. During the day felt indoors by many, outdoors by few. At night some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. Felt by nearly everyone, many awakened. Some dishes, windows, etc., broken; a few instances of cracked plaster; unstable objects overturned. Disturbances of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop. Felt by all, many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged chimneys. Damage slight. Everybody runs outdoors. Damage negligible in building of good design and construction; slight to moderate in well-built ordinary structures; considerable in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving motor cars. Damage slight in specially designed structures; considerable in ordinary substantial buildings, with partial collapse; great in poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Persons driving motor cars disturbed. IX X Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb; great in substantial buildings, with partial collapse. Buildings shifted off foundations. Ground cracked conspicuously. Underground pipes broken. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable from river banks and steep slopes. Shifted sand and mud. Water splashed (slopped) over banks. XI XII Few, if any, (masonry) structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipelines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly. Damage total. Practically all works of construction are damaged greatly or destroyed. Waves seen on ground surface. Lines of sight and level are distorted. Source: California Geological Survey, 2002, How Earthquakes and Their Effects are Measured, Note

7 An estimated earthquake of magnitude 6.9 from the Greenville Fault located approximately 5.5 miles southwest of the project site also would be capable of generating strong to very strong ground shaking (MMI-VII and -VIII, respectively) in the vicinity of the project site (Table 4.6-1). 16 The Greenville Fault has an estimated three percent probability of a magnitude 6.7 or greater earthquake during the period from 2002 to The Concord-Green Valley Fault, located approximately 10 miles west of the project site and the Calaveras Fault located approximately 12 miles southwest of the project site, have estimated four percent and 11 percent probabilities respectively of a magnitude 6.7 or greater earthquake during the period from 2002 to An earthquake of magnitude 6.7 on the Concord-Green Valley Fault or magnitude 6.8 on the Calaveras Fault is estimated to be capable of generating moderate to strong ground shaking (MMI-VI and - VII, respectively) in the vicinity of the project site (Table 4.6-1). 19 Liquefaction Liquefaction is the temporary transformation of loose, saturated, granular sediments to a fluid-like state as a result of seismic ground shaking. In the process, the soil undergoes transient loss of strength, which commonly causes ground displacement such as lateral spreading. Based on factors such as proximity to faults, groundwater level, and soil characteristics, the Association of Bay Area Governments (ABAG) has rated the project site as having a very low liquefaction potential along the ridge slopes of Horse Valley and moderate liquefaction potential along the valley floor. Liquefaction potential is estimated as moderate along the floor of Lone Tree Valley where the utilities and transportation corridor developments are proposed. 20 Landslides Slope failure can occur as either rapid movement of large masses of soil or imperceptibly slow movement of soils on slopes. The primary factors influencing the stability of a slope are the nature of the underlying soil or bedrock, the geometry of the slope (height and steepness), and rainfall. The presence of historic landslide deposits is a good indicator of future landslides. Regional mapping of historic debris flows (rapid moving landslides) in the project vicinity 16 Ibid. 17 United State Geological Survey, 2003, op. cit. 18 Ibid. 19 ABAG, 2004a, op. cit. 20 ABAG, 2004b

8 indicate that future debris flows will likely occur in the west portion of the project site. 21 Regional mapping of slides and earth flows (slow moving landslides) in the project vicinity indicates that small landsides and possibly a few large landslides are possible along the rolling hills and ridge slopes in the northeast, south, and west portions of the project site. Slope failure would not likely impact the valley floor in the north central portion of the project site or along the proposed utilities and transportation corridor, except possibly along stream banks and terrace margins. 22 Geologic Hazards Soil Erosion Soils in the north central portion of the project site along the valley floor are classified as having a slight susceptibility to erosion. 23 Soils along the rolling hills and ridge slopes of the project site are classified as having a moderate to high susceptibility to erosion. No hazard of erosion has been identified along the valley floor of the proposed utilities and transportation corridor. 24 The potential for water-induced erosion is generally increased during the rainy season when soil is exposed to rainfall and storm water runoff. Subsidence Subsidence is often caused by human activities, such as over-pumping groundwater from an aquifer for irrigation. Future use of the project site does not include groundwater extraction and therefore groundwater-related subsidence would not be a project impact. Strong seismic shaking can also cause subsidence of unsaturated, loose granular material or uncompacted fill soils. The presence of abandoned coal mines near the project site presents the potential for surface subsidence from mining tunnel collapse. Collapse of mining voids could cause gradual or sudden subsidence of the ground surface above the tunnels depending on the depths to the tunnels and the intervening bedrock material. Historic mining activities and potential hazards associated with mining tunnel collapse are further discussed below. Caving Soils susceptible to sloughing pose a hazard to construction workers during excavations. Soils identified in the floor of Horse Valley at the project site have a low potential for caving during excavations to a maximum depth of approximately 5 feet below ground surface; soils identified in the rolling hills and ridge slopes of the valley at the project site 21 Ellen et al., Wentworth et al., United Stated Department of Agriculture, 1977, op. cit. 24 Ibid

9 and portions of the proposed utilities and transportation corridor along Deer Valley Road have a high potential for caving during excavation. 25 Expansive and Corrosive Soils Soils at the project site have been classified as generally having a moderate to high shrinkswell potential (expansive soils) and corrosion potential. 26 Shrink-swell potential is a measure of the change in soil volumes relative to moisture content. As water enters between clay mineral layers in the soil, the clay structures swell, causing the soils to expand. As the soil dries and water is released from between the clay layers, the soil shrinks. Expansive soils have the potential to damage buildings, roads, and other structures if not properly treated. Corrosive soils can damage subsurface utilities and structures that are not properly treated. Historical Mining A preliminary evaluation of possible historic mining on the project site was conducted in 2006 by Norfleet Consultants, and this report provides the basis for the evaluation of historical mining summarized in this section. 27 Norfleet reviewed available documents describing coal mining operations in the project vicinity, including records from the State Mineralogist, several master s theses describing the coal mining history in the project vicinity, geotechnical reports of the Domingene Formation, newspapers published in the project vicinity between 1860 and 1890, and a site-specific geophysical study performed on the property immediately north of the project site. Three major veins of lignite coal are located in the northwest trending Domingene Formation, which crosses the northwest portion of the project site. The Black Diamond Vein is located near the bottom of the Domingene, the Clark Vein is located near the top of the Domingene, and the Little Vein is located between the other two veins. The Black Diamond Vein extends beneath the project site and the Little Vein and Clark Vein outcrop on the property to the north of the project site. The three major coal veins range in height from approximately 18 inches to 60 inches and are all overlain by sandstone beds ranging in thickness from approximately 50 to 100 feet. The openings to the Empire, Cochrane, Star, Tuetonia, and Israel mines are located within approximately 300 to 800 feet north of the project site and were operated between approximately 1860 and Figure presents the locations of the historic mines within the project vicinity. The coal mining town of West Hartley was located near the Empire, Cochrane, and Star mines 25 United Stated Department of Agriculture, United Stated Department of Agriculture, 1977, op. cit. 27 Norfleet Consultants, 2006a, op. cit. 28 Norfleet Consultants, 2006a, op. cit. and 2006b

10 approximately 400 feet north of the northwest portion of the project site. The town of West Hartley no longer exists. In 1877, the Empire Coal Railroad was constructed along the approximate alignment of the current Empire Mine Road that borders the north side of project site. 29 Evidence of three other potential mines has been identified between 1,000 and 3,000 feet to the north and east, respectively, of the northeast portion of the project site. 30 The entrance and main slope to the Empire, Cochrane, Tuetonia, and Israel mines were excavated down a dip to the north parallel to and just below the coal vein. 31 The main slope would extend between 200 and 400 feet down the dip. At the base of the main slope, two gangways would extend perpendicular to the main slope just below the coal vein. The coal vein was then mined from the bottom up. Individual rooms were mined about 300 feet long, 15 to 30 feet wide, and 3 to 4 feet high using the room and pillar technique. Wood pillars were used to support the roof of the coal bed from collapsing in each room. Pillars of coal about 10 to 20 feet wide also were left between rooms for structural support, but were typically retreat-mined as the room was mined out. One or more ventilation shafts about 2 to 4 feet in diameter were likely excavated to the surface of each mine. 32 Cross tunnels excavated south from the bottom of the main slope may have been used in the Empire and Cochrane Coal mines to access the deeper coal veins. If cross tunnels were used to access the Black Diamond Vein, then mining activities from the Empire and Cochrane Coal mines could have extended beneath the northwest portion of the project site 33 The main slope of the Star Mine was excavated south to cut across the three major coal veins (called a counter slope). At the bottom of the counter slope, a tunnel was excavated north and south to intersect the Black Diamond and Little Veins. According to the preliminary evaluation of possible historic mining in the project area, mining of the Black Diamond Vein may have extended beneath the northwest portion of the project site. Mining of the Black Diamond Vein beneath the project site from the Empire, Cochrane, or Stare mines, if it occurred, would have ceased within 50 to 100 feet below the ground surface of the project site due to the increasingly deteriorated quality of coal located close to the surface. 34 The coal veins are overlain by approximately five feet of weak bedrock material that is susceptible to collapse, which is then overlain by competent bedrock that is not susceptible to collapse ENGEO Inc., ENGEO Inc., ENGEO Inc., 2006 and Norfleet Consultants 2006a, op. cit. 32 Norfleet Consultants, 2006a, op. cit. and 2006b, op. cit. 33 Norfleet Consultants, 2006a, op. cit. 34 Ibid. 35 Figuers,

11 Based on Norfleet Consultant s review of available documents and publications regarding the coal mines in the project vicinity, no entrances to any coal mines on the project site were identified. One or more ventilation shafts from the Empire, Cochrane, and/or Star mines may have been excavated on the northwest portion the project site. 36 Oil and Gas Wells The California Department of Conservation, Division of Oil, Gas, and Geothermal Resources (DOGGR) mapped three plugged and abandoned dry oil/gas wells on the project site. Two of the abandoned wells are located in the West Phase of the project site and the third well is located in the southeast corner of the project site in the vicinity of the proposed Hotel/Villa Phase. It is uncertain whether proposed housing would be located immediately across abandoned dry wells, because the specific locations of the wells have not been surveyed. Eight other oil/gas wells were identified in or in close proximity to the proposed utilities and transportation corridor, as shown in Figure These include three oil wells, three gas wells, and two dry wells. All of the wells on the project site and along the utilities and transportation corridor have been plugged and abandoned. 37 One oil/gas well has been proposed (but is not yet constructed) on the adjacent property north of the project site; construction and operation of this well would not likely affect project development. Section 4.7, Hazards and Hazardous Materials, provides a discussion regarding the verification of properly plugged wells in the project vicinity. Plugging and abandoning wells to the current DOGGR standards reduces the potential for wells to start leaking oil, gas, and/or water after abandonment. DOGGR requires the well casings of abandoned wells to be cut between 5 and 10 feet below ground surface; therefore, the abandoned wells at the project site may not be visible on the ground surface. Development over an abandoned well is discouraged by DOGGR to reduce potential impacts to public health and safety. Historic drilling activities for oil wells may have generated mud pits that contain petroleum hydrocarbons. 38 Mud pits, if present, would be distinctly different than native soil formations at the project site. Hazardous materials associated with oil drilling activities are discussed further in Section 4.7, Hazards and Hazardous Materials. High-Voltage Transmission Lines, Gas and Liquid Fuel Pipelines, and Flammable Storage Facilities High-voltage transmission lines and flammable storage facilities are not located on the project site. A gas pipeline is located along Deer Valley Road adjacent to the project site. 36 Norfleet Consultants, 2006b, op. cit. 37 Department of Conservation, Department of Conservation,

12 oad Min er ire De er Valley Road p Em Star Mine Empire Mine Teutonia Mine Cochrane Mine Israel Mine Possible Mine Mine Opening Empire Mine Road Open Mine Tunnel LEGEND Balfour Road Har ri s Ra nc Chadbourne Road whole view. SM Not to scale Source: BASELINE Environmental, 2008;, hr oad PROJECT BOUNDARY MINE LOCATIONS PROPOSED WATER LINE PROPOSED SEWER LINE PROPOSED STORM DRAIN LINE PROPOSED NON-POTABLE WATER LINE ARTERIAL IMPROVEMENTS TO DEER VALLEY ROAD POTENTIAL AREA OF DISTURBANCE *DASHED LINES REPRESENT EXISTING UTILITIES PERLIMINARY LOCATIONS AND SIZING NOTE: ALL PROPOSED UTILITY LOCATIONS AND SIZES ARE APPROXIMATE FIGURE HISTORIC MINE LOCATIONS

13 Heidorn Ranch Road Road M ire ine De er Valley Road p Em Sand Creek Road LEGEND Empire Mine Road Balfour Road Har ri s PROJECT BOUNDARY PLUGGED/ABANDONED DRY WELL PLUGGED/ABANDONED OIL WELL PLUGGED/ABANDOND GAS WELL PROPOSED WATER LINE PROPOSED SEWER LINE PROPOSED STORM DRAIN LINE PROPOSED NON-POTABLE WATER LINE ARTERIAL IMPROVEMENTS TO DEER VALLEY ROAD POTENTIAL AREA OF DISTURBANCE Ra nc hr oad Chadbourne Road whole view. SM Not to scale Source: BASELINE Environmental, 2008;, *DASHED LINES REPRESENT EXISTING UTILITIES PERLIMINARY LOCATIONS AND SIZING NOTE: ALL PROPOSED UTILITY LOCATIONS AND SIZES ARE APPROXIMATE FIGURE OIL AND GAS WELL LOCATIONS

14 Two other gas pipelines and two liquid hazard pipelines are located across the alignment of the proposed utilities and transportation corridor. 39 Mineral Resources Mineral Land Classification Maps published by the State of California 40 classify land in the project site as Mineral Resource Zone (MRZ)-1, MRZ-3, and MRZ-4, indicating that significant mineral deposits have not been identified or determined at the project site. The proposed utilities and transportation corridor is predominantly classified as a MRZ-1, which indicates that significant mineral resources have not been identified. These zones are shown in Figure Regulatory Setting Seismic Hazards Alquist-Priolo Earthquake Fault Zoning Act The Alquist-Priolo Earthquake Fault Zoning Act regulates development in California near known active faults due to hazards associated with surface fault ruptures. The Earthquake Fault Zones indicate areas with potential surface fault-rupture hazards, and specific geological investigations are required prior to development. Seismic Hazard Mapping Act The Seismic Hazard Mapping Act was passed in 1990 following the Loma Prieta earthquake to reduce threats to public health and safety and to minimize property damage caused by earthquakes. The Act directs the U.S. Department of Conservation to identify and map areas prone to the earthquake hazards of liquefaction, earthquake-induced landslides, and amplified ground shaking. The act requires site-specific geotechnical investigations to identify potential seismic hazards and formulate mitigation measures prior to permitting most developments designed for human occupancy within the Zones of Required Investigation. The Seismic Hazard Map for the vicinity of the project site is currently under preparation and is not available for review. California Building Code The 2007 California Building Code (CBC) covers grading and other geotechnical issues, building specifications, and non-building structures. The CBC requires that a site-specific geotechnical report be prepared by a licensed professional for proposed developments of 39 United States Department of Transportation Office of Pipeline Safety, Kohler et al.,

15 Mineral Resource Zone (MRZ) Boundaries MRZ-1* Areas where adequate information indicates that no mineral deposits are present, of where it is judged that little likelihood exists for their presence MRZ-2* Areas where adequate information indicates that mineral deposits are present, of where it is judged that a high likelihood exists for their presence MRZ-3* Areas containing mineral deposits the of which cannot be evaluated from available data MRZ-4* Areas where available information is inadequate for assignment to any other MRZ zone Transportation and Utility Corridors Project Site SM FIGURE whole view. Source: ENGEO Incorporated, MINERAL RESOURCES

16 one or more buildings greater than 4,000 square feet to evaluate geologic and seismic hazards. Buildings less than or equal to 4,000 square feet also are required to prepare a geologic engineering report, except for one-story, wood-frame, and light-steel-frame buildings of Type II or Type V construction that are located outside of the Alquist-Priolo Earthquake Faults Zones and CGS Seismic Hazard Zones. The site-specific geotechnical report shall provide measures to reduce potentially significant seismic hazards such as surface fault ruptures, ground shaking, liquefaction, and seismically-induced slope failures and settlement, regardless of the proposed grading on slopes. The geotechnical report would be reviewed by the City of Antioch Building Division prior to issuance of building permits to ensure compliance. City of Antioch Municipal Code The City of Antioch shall not issue a building permit unless the application complies with the 2007 CBC and other pertinent laws and ordinances of the City or any other governmental body having jurisdiction within the City. 41 City of Antioch General Plan The Environmental Hazards Element of the City of Antioch General Plan contains the following policies and objectives related to seismicity. Policy a Require geologic and soils reports to be prepared for proposed development sites, and incorporate the findings and recommendations of these studies into project development requirements. As determined by the City of Antioch Building Division, a site-specific assessment shall be prepared to ascertain potential ground shaking impacts on new development. The site-specific ground shaking assessment shall incorporate up-to-date data from government and nongovernment sources and may be included as part of any site-specific geotechnical investigation. The site-specific ground shaking assessment shall include specific measures to reduce the significance of potential ground shaking hazards. This sitespecific ground shaking assessment shall be prepared by a licensed geologist and shall be submitted to the City of Antioch Building Division for review and approval prior to the issuance of building permits. For purposes of this policy, development applies to new structures and existing structures or facilities that undergo expansion, remodeling, renovation, refurbishment, or other modification. This policy does not apply to second units or accessory buildings. Policy e Provide expedited review of any seismic-related revisions to the Uniform Building Code proposed by the State. 41 City of Antioch,

17 Policy f Work with PG&E, pipeline companies, and industrial uses to implement measures to safeguard the public from seismic hazards associated with high-voltage transmission lines, caustic and toxic gas and fuel lines, and flammable storage facilities. Policy g Require that engineered slopes be designed to resist seismically-induced failure. Policy h Require that parcels overlying both cut and fill areas within a grading operation be over-excavated to mitigate the potential for seismicallyinduced differential settlement. Geologic Hazards California Building Code The CBC requires that a site-specific geotechnical report be prepared by a licensed professional to evaluate geologic and seismic hazards on proposed developments, as discussed above. The site-specific geotechnical report shall provide measures to reduce potentially significant geologic hazards, such as expansive and corrosive soils, differential settlement, and slope stability. The geotechnical report shall be reviewed by the City of Antioch Building Division prior to issuance of building permits. California Division of Occupational Safety and Health The California Division of Occupational Safety and Health (DOSH) regulations are aimed at protecting workers and the public from safety hazards. The California DOSH requires adequate protection from potential caving during all excavations, such as the installation of protective barricades along the walls of the excavation. Division of Oil, Gas, and Geothermal Resources DOGGR regulates oil and gas drilling activities. DOGGR assists in locating and reviewing the status of oil and gas wells located near or beneath proposed developments. DOGGR requires the owner of the property to provide and maintain access to all oil and gas wells in order for the DOGGR to evaluate and repair the wells should future problems arise; otherwise, the owner of the property will be held responsible for potential future reabandonment costs. United States Department of Transportation s Office of Pipeline Safety The United States Department of Transportation s Office of Pipeline Safety (OPS) is the lead federal regulator of pipeline safety. Gas and hazardous liquid pipelines have been subject to federal pipeline safety and maintenance regulations since the Natural Gas Pipeline Safety Act of 1968 and the Hazardous Liquid Pipeline Safety Act of Federal pipeline safety regulations are covered in Title 49 of the Federal Code of Regulations

18 (Parts ) and additional state regulations are covered in the California Government Code Section The California Public Utilities Commission s Utilities Safety and Reliability Branch (USRB) and the State Fire Marshal have been granted authority by the OPS to oversee the enforcement of safety regulations for natural gas and hazardous liquid pipelines in California. Federal and state regulations require operators of gas and hazardous liquid pipelines in high-consequence areas to conduct a risk analysis and implement integrity management programs. High-consequence areas include populated and environmentally sensitive areas as defined by the Federal Code of Regulations (Parts 192 and 195). Integrity management plans include implementing preventive measures to protect highconsequence areas and enhance public safety from pipeline failure, such as installing lowpressure alarms, emergency flow-restricting devices, automatic safety shut-off valves, and computerized monitoring and leak detection systems. The integrity management programs continually assess and evaluate pipeline safety, as well as identify and incorporate newly populated areas. Underground Service Alert Underground Service Alert is the regional notification center for proposed excavations in northern California. California Government Code Section 4216 requires that the appropriate regional notification center be contacted between two and 14 days prior to any excavations in an area where subsurface utilities could potentially be present. Any operator of a subsurface utility in the proposed excavation area shall mark out the approximate locations of the utilities in the field within two working days of notification. If an excavation is proposed within 10 feet of a high-priority subsurface installation, such as a high pressure natural gas or petroleum pipeline, the operator of the high-priority installation must notify the excavator and hold an onsite meeting to verify the location of the installation. City of Antioch Municipal Code As discussed above, the City of Antioch shall not issue a building permit unless the application complies with the 2007 CBC and other pertinent laws and ordinances of the City or any other governmental body having jurisdiction within the City. 42 City of Antioch General Plan The Environmental Hazards Element of the City of Antioch General Plan contains the following policies and objectives related to geologic hazards. 42 City of Antioch, 2008, op. cit

19 Policy i Limit development in those areas, which, due to adverse geological conditions, will be hazardous to the overall community and those who will inhabit the area. Policy j Require evaluations of potential slope stability for developments proposed within hillside areas, and incorporate the recommendations of these studies into project development requirements. Policy k Require specialized soils reports in areas suspected of having problems with potential bearing strength, expansion, settlement, or subsidence, including implementation of the recommendations of these reports into the project development. Policy l Where development is proposed within an identified or potential liquefaction hazard area (as determined by the City), adequate and appropriate measures such as (but not limited to) designing foundations in a manner that limits the effects of liquefaction, the placement of an engineered fill with low liquefaction potential, and the alternative siting of structures in areas with a lower liquefaction risk, shall be implemented to reduce potential liquefaction hazards. Any such measures shall be submitted to the City of Antioch Building Division for review prior to the approval of the building permits. Policy m As appropriate and necessary to protect public health and safety, abandoned mines shall be placed in natural open space areas, with appropriate buffer areas to prevent unauthorized entry. Policy n Within areas of known historic mining activities, site-specific investigations shall be undertaken prior to approval of development to determine the location of any remaining mine openings, the potential for subsidence of collapse, and necessary measures to protect public health and safety, and prevent the collapse or structural damage to structures intended for human occupancy due to mine-related ground failure or subsidence. Such measures shall be incorporated into project approvals. Policy o. All identified mine openings shall be effectively sealed. Policy p. Construction of structures for human occupancy shall be prohibited within areas found to have a high probability of surface collapse or subsidence, unless foundations are designed that would not be affected by such surface collapse or subsidence, as determined by site-specific investigations and engineered structural design. Policy q. The locations of all oil or gas wells on proposed development sites shall be identified in development plans. Project sponsors of development containing existing or former oil or gas wells shall submit documentation

20 Mineral Resources demonstrating that all abandoned wells have been properly abandoned pursuant to the requirements of the California Department of Conservation, Oil, Gas, and Geothermal Resources. Surface Mining and Reclamation Act In compliance with the Surface Mining and Reclamation Act, the State Mining and Geology Board has designated mineral resources in areas within California subject to irreversible land uses that would preclude mineral extraction. Land has been classified by the State Geologist into Mineral Resource Zones (MRZs) based on geologic and economic factors. Mineral Resource Zones include classification for construction materials, industrial and chemical mineral materials, metallic and rare minerals, and non-fluid mineral fuels. The mapping of MRZs is intended to help identify and preserve significant mineral deposits for future use. Mineral Resource Zones are defined as follows: MRZ-1 = Areas where adequate information indicates that no significant mineral deposits are present, or it is judged that little likelihood exists for their presence; MRZ-2 = Areas where adequate information indicates that significant mineral deposits are present, or where it is judged that a high likelihood exists for their presence; MRZ-3 = Areas containing known or inferred mineral deposits of which the significance is undetermined based on available data; and MRZ-4 = Areas where available information is inadequate for assignment to any other MRZ zone. Policy Consistency Analysis The project would be consistent with the City of Antioch General Plan policies with regard to geology and soils. Policies a, e, g, h, i, j, k, l, and p are addressed by the current 2007 CBC standards, which are required by the City of Antioch. Seismic hazards associated with high-voltage transmission lines and flammable storage facilities do not apply to the project, as discussed in Policy f. The OPS requirements for operators of gas and hazardous liquid pipelines to conduct risk assessments and implement safety measures for pipeline segments adjacent to populated and environmentally sensitive areas comply with Policy f for the project. Prior to excavations for the project site and the proposed utilities and transportation corridor, Underground Services Alert must be notified to coordinate the mark-out of subsurface utilities

21 In accordance with Policies m, n, and o, previous investigations of historic mining activities have been performed at the project site and nearby properties and potential impacts from mining activities are discussed further, in Section 4.6.2, Impacts and Mitigation Measures, of this EIR. The potential impacts from former oil or gas wells related to Policy q are also discussed in Section 4.6.2, Impacts and Mitigation Measures, of this EIR IMPACTS AND MITIGATION MEASURES Significance Criteria Appendix G of the CEQA Guidelines identified environmental issues to be considered when determining whether a project could have significant effects on the environment. As identified in Appendix G, the project would have significant agricultural impacts if it would: a. Expose people, buildings, or infrastructure to potential substantial adverse effects, including the risk of loss, injury, or death involving: i. Rupture of a known earthquake fault, as delineated on the most recent Alquist- Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault; ii. Strong seismic shaking; iii. Seismic-related ground failure, including liquefaction; iv. Landslides; b. Result in substantial soil erosion or the loss of topsoil (changes in topography or unstable soil conditions from excavation, grading or filling); c. Be located on a geologic unit or soil that is unstable or that would become unstable as a result of the project, and potentially result in on- or off-site landslide, lateral spreading, subsidence, liquefaction or collapse; d. Be located on expansive soil, as defined in Table 18-1-B of the Uniform Building Code (1994), creating substantial risks to life or property; e. Have soils incapable of adequately supporting the use of septic tanks or alternative wastewater disposal systems where sewers are not available for the disposal of waste water; f. Result in the loss of availability of a known mineral resource that would be of value to the region and the residents of the State; or

22 g. Result in the loss of availability of a locally important mineral resource recovery site delineated on a local general plan, specific plan or other land use plan. Less Than Significant Impacts Seismic Hazards The project site is not located in an Alquist-Priolo Earthquake Fault Zone. Therefore, impacts associated with surface fault rupture at the project site are less than significant. The project site is potentially susceptible to seismically-generated ground shaking, liquefaction, slope failure, and subsidence. The City of Antioch ordinances require a sitespecific geotechnical investigation prepared by a licensed professional addressing seismic hazards in accordance with the 2007 CBC standards to provide measures that will reduce potentially significant impacts to proposed structures and people present at the project site. The policies of the City s General Plan relating to seismicity also require a sitespecific geotechnical report for seismic hazards that could impact new development. The General Plan policies include designing engineered slopes to resist seismically induced failure and over-excavating cut and fill areas to reduce the potential for seismically induced subsidence. Structures built in accordance with modern seismic design criteria, as included in the 2007 CBC standards, are much more likely to withstand the expected seismic hazards associated with a large earthquake than older buildings. Incorporation of the findings and recommendations of a site-specific geotechnical investigation into the project development plans, as required by the City of Antioch, would reduce potentially significant impacts related to seismically-generated ground shaking, liquefaction, slope failure, and subsidence on development infrastructure, structures, and future users of the project site to a less than significant level. Geologic Hazards Soils at the project site are susceptible to erosion. Compliance with erosion control measures, as required by the National Pollutant Discharge Elimination System (NPDES) program, would reduce the potential impacts related to soil erosion to a less-thansignificant level. Refer to Section 4.8, Hydrology and Water Quality, for further discussion regarding erosion control requirements. Subsidence from ground water extraction would have no related impacts since ground water extraction is not proposed. Soils at the project site and the proposed utilities and transportation corridor have a high potential for caving during excavation. Compliance with DOSH requirements would reduce this potentially significant impact to a less-thansignificant level

23 Soils at the project site are susceptible to expansion and corrosion. The City of Antioch ordinances require a site-specific geotechnical investigation prepared by a licensed professional addressing geologic hazards in accordance with the 2007 CBC standards. The policies of the General Plan relating to geologic hazards also require a site-specific geotechnical report for soils that could impact structures and/or human occupants, such as expansive and corrosive soils. Incorporation of the findings and recommendations of a site-specific geotechnical investigation for soil hazards into the project development plans, as required by the City of Antioch, would reduce potential significant impacts associated with expansive and corrosive soils to a less than significant level. There are no known outcrops indicating unique geological features at the project site. Therefore, grading activities for the project would have a less than significant impact on unique geological features. Mineral Resources Significant mineral deposits have not been identified at the project site by the State Mining and Geology Board (SMGB). Development of the project would therefore have a less than significant impact on the availability of locally and statewide valuable minerals. Significant Impacts Geologic Hazards Impact 4.6-1: Mine hazards could jeopardize safety of workers/people on the project site Based on the preliminary evaluation of possible historic mining conducted by Norfleet Consultants in 2006, coal mine tunnels may extend beneath the northwest side of the project site from abandoned mines located north of the project site. 43 The mine tunnels would likely cease approximately 50 to 100 feet below the ground surface of the project site. The potential for surface subsidence from any mining activity beneath undisturbed bedrock at the project site would be remote because the tunnels are generally less than 4 feet in height and overlain by competent bedrock; however, construction grading activities that may decrease the thickness of competent bedrock or excavate through the competent bedrock overlaying an abandoned coal mine could potentially pose a significant hazard to construction workers and/or other people present at the project. One or more ventilation shafts may also be present at the project site from mining activities that could potentially pose a significant hazard to construction workers and/or other people present at the project site. Mitigation Measure 4.6-1: The applicant shall incorporate all findings and recommendations of a final site-specific design-level geotechnical investigation, 43 Norfleet Consultants, 2006b, op. cit